OS/400 is IBM's operating system for its AS/400 and AS/400e line of business computers. Because OS/400 is closely attuned to the AS/400 hardware design and generally comes as part of the basic package, there is no alternative operating system to compete with it. OS/400 is built to operate with the AS/400 logical partition (LPAR) architecture, in which multiple instances of the operating system can run concurrently in different partitions. Among other uses, LPAR is useful when migrating to a new release. The old production system can keep operating in one partition while a new system is being tested.